U.S. patent application number 12/333219 was filed with the patent office on 2009-06-18 for method and apparatus for reading test strips.
This patent application is currently assigned to Arbor Vita Corporation. Invention is credited to Michael P. Belmares, Joseph Byerly, Christopher Kepner, Peter S. Lu, Johannes Schweizer, Thomas M. Sherlock.
Application Number | 20090155921 12/333219 |
Document ID | / |
Family ID | 40753791 |
Filed Date | 2009-06-18 |
United States Patent
Application |
20090155921 |
Kind Code |
A1 |
Lu; Peter S. ; et
al. |
June 18, 2009 |
METHOD AND APPARATUS FOR READING TEST STRIPS
Abstract
The present invention provides a method and apparatus for
reading test strips such as lateral flow test strips as used for
the testing of various chemicals in humans and animals. A compact
and portable device is provided that may be battery powered when
used remotely from the laboratory and, may store test data until it
can be downloaded to another database. Motive power during scanning
of the test strip is by means of a spring and damper that is wound
by the operator during the insertion of a test strip cassette
holder prior to test.
Inventors: |
Lu; Peter S.; (Mountain
View, CA) ; Byerly; Joseph; (Pebble Beach, CA)
; Kepner; Christopher; (Campbell, CA) ; Sherlock;
Thomas M.; (Los Altos, CA) ; Belmares; Michael
P.; (San Jose, CA) ; Schweizer; Johannes;
(Mountain View, CA) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER, EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Arbor Vita Corporation
Sunnyvale
CA
|
Family ID: |
40753791 |
Appl. No.: |
12/333219 |
Filed: |
December 11, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61013634 |
Dec 13, 2007 |
|
|
|
61013299 |
Dec 12, 2007 |
|
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Current U.S.
Class: |
436/164 ;
422/400 |
Current CPC
Class: |
G01N 21/274 20130101;
G01N 2201/12792 20130101; G01N 21/276 20130101; G01N 21/8483
20130101 |
Class at
Publication: |
436/164 ;
422/55 |
International
Class: |
G01N 21/75 20060101
G01N021/75; G01N 21/00 20060101 G01N021/00 |
Claims
1. A test strip reader, comprising: a light source that illuminates
at least part of a test strip; a transport mechanism that moves the
test strip past the light source, the transport mechanism further
comprising a spring that propels the test strip and a damping
mechanism that limits the speed of transport; a sensor that
produces a signal indicating the intensity of light reflected from
the test strip; electronic circuitry configured to repeatedly
measure the signal from the sensor and to produce for each
measurement a digital value representing the reflected light
intensity; a processor configured to determine, based on the
digital values, a test result.
2. The test strip reader of claim 1, wherein the sensor is a first
sensor, the test strip reader further comprising a second sensor
that produces a signal indicating the brightness of the light
source, and wherein the electronic circuitry is further configured
to also measure the signal from the second sensor and to adjust the
digital values to compensate for variability of the brightness of
the light source.
3. The test strip reader of claim 2, wherein the second sensor
senses the brightness of the light source directly.
4. The test strip reader of claim 2, wherein the second sensor
senses the intensity of light reflected from a reference strip.
5. The test strip reader of claim 4, wherein the reference strip is
also moved by the transport mechanism.
6. The test strip reader of claim 1, further comprising a battery,
and wherein the electronic circuitry is powered using energy from
the battery.
7. The test strip reader of claim 1, further comprising an
indicator that indicates the test result.
8. The test strip reader of claim 1, further comprising an encoder
that indicates progress of the transport mechanism by producing a
series of position-indicating signals related to the position of
the transport mechanism, and wherein the measurements of light
intensity signal occur upon receipt by the electronic circuitry of
at least some of the position-indicating signals.
9. The test strip reader of claim 1, further comprising a bar code
reader that reads a bar code from a cassette holding the test
strip.
10. The test strip reader of claim 9, wherein the test strip and
the bar code reside on opposite sides of the cassette.
11. The test strip reader of claim 1, further comprising a display
upon which test results are displayed.
12. The test strip reader of claim 11, wherein the display is a
liquid crystal display.
13. The test strip reader of claim 11, wherein the display is a
touch screen display.
14. The test strip reader of claim 1, further comprising at least
one input/output port connector.
15. The test strip reader of claim 14, wherein the electronic
circuitry further comprises a memory in which test data are stored
for later communication to an external computer system via at least
one input/output connector.
16. The test strip reader of claim 11, further comprising a
removable memory into which test data are stored.
17. The test strip reader of claim 1, wherein a reading optical
system directs light reflected from the test strip to the
sensor.
18. The test strip reader of claim 17, wherein the reading optical
system comprises at least one lens element.
19. The test strip reader of claim 17, wherein the reading optical
system comprises at least one spherical lens element.
20. The test strip reader of claim 19, wherein the spherical lens
element comprises a transmission band having a polished surface,
and wherein the remainder of the surface of the spherical lens
element is configured to reduce stray light reflections.
21. The test strip reader of claim 20, wherein the remainder of the
surface of the spherical lens element has a matte finish and is
covered with a light-absorbing coating.
22. The test strip reader of claim 17, wherein the reading optical
system further comprises a semi-cylindrical lens proximate the
sensor.
23. The test strip reader of claim 1, further comprising an
aperture placed immediately in front of the sensor.
24. The test strip reader of claim 23, wherein the aperture is a
slit aperture having a width of between 0.025 inches and 0.035
inches (0.64 millimeters and 0.89 millimeters).
25. The test strip reader of claim 1, wherein the damping mechanism
is a rotary damper.
26. The test strip reader of claim 1, wherein the light source
illuminates the test trip from a direction substantially
perpendicular to the test strip surface.
27. A test strip reader, comprising: a light source that
illuminates at least part of a test strip; a mechanically-powered
transport mechanism that moves the test strip past the light
source; electronic circuitry comprising a processor and configured
to repeatedly measure a quantity of light reflected from the test
strip, to produce for each measurement a digital value representing
the measured light quantity, and to determine a test result based
on the digital values; and a battery that supplies power to the
light source and electronic circuitry.
28. A method of ascertaining a test result, comprising: receiving a
test strip to which a test fluid has been applied; reading the
reflectance of the test strip at multiple locations along the test
strip by mechanically transporting the test strip past a reading
location in a battery-powered test strip reader; recording a
digital value for each reflectance reading; ascertaining a peak or
minimum reflectance value in each of one or more regions of the
test strip; comparing the peak or minimum reflectance values with a
predetermined set of interpretation rules to determine the test
outcome; and communicating the test outcome.
29. The method of claim 28, wherein transporting the test strip
further comprises moving a tray carrying the test strip under the
action of a spring, the method further comprising limiting the
speed of transport by a mechanical damper actuated by motion of the
tray.
30. The method of claim 28, wherein reading the reflectance of the
test strip further comprises: illuminating the test strip; and
reading an intensity of light reflected from the test strip.
31. A test strip reader, comprising: a base portion housing a
mechanical transport mechanism including a spring and a damper; an
upper portion housing an illumination source that illuminates a
test strip under test, a sensor that detects light reflected from
the test strip, an electronic circuit that controls operation of
the test strip reader, and a display on which test results are
shown to a user of the test strip reader; wherein the test strip
under test resides above the base portion, and is transported by
the transport mechanism beneath the light source during reading of
the test strip.
32. The test strip reader of claim 31, wherein the display is
positioned at an angle of between 30 and 60 degrees from
horizontal.
33. The test strip reader of claim 31, further comprising an
encoder that produces signals indicating a position of the
transport mechanism, and wherein the intensity of the light
reflected from the test strip is measured upon receipt by the
electronic circuit of at least some of the position-indicating
signals.
34. The test strip reader of claim 31, wherein the display is a
touch screen display.
35. The test strip reader of claim 31, further comprising a movable
tray that holds a cassette, which in turn holds the test strip
under test.
36. The test strip reader of claim 35, wherein the movable tray is
configured to accommodate cassettes of different sizes and from
different test manufacturers.
37. The test strip reader of claim 35, further comprising: a gear
rack on the movable tray; and a rotary damper in the base portion
including a pinion gear; wherein the gear rack engages the pinion
gear during reading of the test strip.
38. The test strip reader of claim 31, further comprising a bar
code reader in the base portion, wherein the barcode reader reads a
barcode from a cassette that holds the test strip in con unction
with reading of the test strip.
39. The test strip reader of claim 31, wherein the light source is
a light emitting diode.
40. The test strip reader of claim 31, further comprising an
illumination optical system that enhances the level of illumination
of the test strip.
41. The test strip reader of claim 40, wherein the illumination
optical system comprises at least one spherical lens element and at
least one hemispherical lens element.
42. The test strip reader of claim 31, further comprising a reading
optical system that directs at least some of the light reflected
from the test strip to the sensor.
43. The test strip reader of claim 42, wherein the reading optical
system comprises at least one spherical lens element.
44. The test strip reader of claim 42, wherein the reading optical
system comprises at least one semi-cylindrical lens element.
45. The test strip reader of claim 31, wherein the sensor is a
first sensor, and further comprising a second sensor that senses
illumination from the light source directly, and wherein the
electronic circuit is configured to adjust measurements of
reflected light taken from the first sensor, based on direct
measurements of light intensity taken from the second sensor, to
compensate for variations in the intensity of the light source
during reading of the test strip.
46. The test strip reader of claim 31, further comprising a battery
that powers the electronic circuitry.
47. The test strip reader of claim 31, wherein the electronic
circuitry is configured to repeatedly take measurements of the
light reflected from the test strip during reading of the test
strip, convert the measurements to digital values, and to apply a
predetermined set of interpretation rules to the digital values in
order to determine a test result.
48. The test strip reader of claim 31, wherein the electronic
circuitry comprises removable memory in which test data are stored.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. provisional
application 61/013,299 filed on Dec. 12, 2007 entitled "Method and
Apparatus for Reading Test Strips" and U.S. provisional application
61/013,634 filed on Dec. 13, 2007 entitled "Method and Apparatus
for Reading Test Strips", and the content of both of these
applications is hereby incorporated by reference in its entirety
and for all purposes.
BACKGROUND OF THE INVENTION
[0002] Test strips, as used in the detection of pregnancy,
infection, drugs or other constituents of human fluids, can be read
by eye or by machine. Some tests, by their nature are easily read
by eye because the chemical reaction between the components on the
test strip causes great enough color changes at specific points on
the strip that the contrast with the background is easily visually
discernable Other strip tests are more appropriately read by
machine if the contrast between an area of indication and the
background is slight or if the decision as to whether a test is
positive or negative rests in an algorithm that compares relative
reflectance values of multiple areas along the test strip.
Typically, the devices that read test strips are expensive and
relatively large, restricting their use to the lab or clinical
setting.
BRIEF SUMMARY OF THE INVENTION
[0003] The present invention provides a portable device for
accurately determining a test result from a test strip. Such a test
strip reader comprises a light source that illuminates at least
part of a test strip; a transport mechanism that moves the test
strip past the light source, the transport mechanism further
comprising a spring that propels the test strip and a damping
mechanism that limits the speed of transport; a sensor that
produces a signal indicating the intensity of light reflected from
the test strip; electronic circuitry configured to repeatedly
measure a quantity of light reflected from the test strip and to
produce for each measurement a digital value representing the
measured light quantity; and a processor configured to determine,
based on the digital values, a test result. In some embodiments,
the sensor is a first sensor, and the test strip reader further
comprises a second sensor that produces a signal indicating the
brightness of the light source, and the electronic circuitry is
further configured to also measure the signal from the second
sensor and to adjust the digital values to compensate for
variability of the brightness of the light source. The second
sensor may sense the brightness of the light source directly, or
may sense the intensity of light reflected from a reference strip.
The reference strip may also be moved by the transport
mechanism.
[0004] The test strip reader may further comprise a battery that
powers the electronic circuitry. The test strip reader may comprise
an indicator that indicates the test result. The test strip reader
may comprise an encoder that indicates progress of the transport
mechanism by producing a series of position-indicating signals
related to the position of the transport mechanism, and the
measurements of light intensity signal may occur upon receipt by
the electronic circuitry of at least some of the
position-indicating signals. The test strip reader may comprise a
bar code reader that reads a bar code from a cassette holding the
test strip. The test strip and bar code may reside on opposite
sides of the cassette.
[0005] The test strip reader may further comprise a display upon
which test results are displayed. The display may be a liquid
crystal display, and may be a touch screen display. The test strip
reader may comprise at least on input/out port connector. The test
strip reader electronic circuitry may further comprise a memory in
which test data are stored for later communication to an external
computer system via at least one of the input/output connector. The
test strip reader may comprise a removable memory.
[0006] The test strip reader may comprise a reading optical system
that directs light reflected from the test strip to the sensor, and
the reading optical system may comprise at least one lens element.
The reading optical system may comprise at least one spherical lens
element. The spherical lens element may comprise a transmission
band having a polished surface, and the remainder of the surface of
the spherical lens element may be configured to reduce stray light
reflections. The remainder of the surface of the spherical lens
element may have a matte finish and may be covered with a
light-absorbing coating. The reading optical system may comprise a
semi-cylindrical lens element proximate the sensor, and may
comprise an aperture placed immediately in front of the sensor. The
aperture may be a slit aperture having a width of between 0.025
inches and 0.035 inches (0.64 millimeters and 0.89
millimeters).
[0007] The damping mechanism may be a rotary damper. The light
source may illuminate the test strip from a direction substantially
perpendicular to the test strip surface.
[0008] In another embodiment, a test strip reader comprises a light
source that illuminates at least part of a test strip; a
mechanically-powered transport mechanism that moves the test strip
past the light source; electronic circuitry comprising a processor
and configured to repeatedly measure a quantity of light reflected
from the test strip, to produce for each measurement a digital
value representing the measured light quantity, and to determine a
test result based on the digital values; and a battery that
supplies power to the light source and electronic circuitry.
[0009] In another embodiment, a method of ascertaining a test
result comprises receiving a test strip to which a test fluid has
been applied; reading the reflectance of the test strip at multiple
locations along the test strip by mechanically transporting the
test strip past a reading location in a battery-powered test strip
reader; recording a digital value for each reflectance reading;
ascertaining a peak or minimum reflectance value in each of one or
more regions of the test strip; comparing the peak or minimum
reflectance values with a predetermined set of interpretation rules
to determine the test outcome; and communicating the test outcome.
Transporting the test strip further may further comprise moving a
tray carrying the test strip under the action of a spring, and the
method may further comprise limiting the speed of transport by a
mechanical damper actuated by motion of the tray. The method may
further comprise illuminating the test strip and reading an
intensity of light reflected from the test strip.
[0010] In another embodiment, a test strip reader comprises a base
portion housing a mechanical transport mechanism including a spring
and a damper; an upper portion housing an illumination source that
illuminates a test strip under test, a sensor that detects light
reflected from the test strip, an electronic circuit that controls
operation of the test strip reader, and a display on which test
results are shown to a user of the test strip reader. The test
strip under test resides above the base portion, and is transported
by the transport mechanism beneath the light source during reading
of the test strip. The display may be positioned at an angle of
between 30 and 60 degrees from horizontal. The test strip reader
may further comprise an encoder that produces signals indicating a
position of the transport mechanism, and the intensity of the light
reflected from the test strip may be measured upon receipt by the
electronic circuit of at least some of the position-indicating
signals.
[0011] The display may be a touch screen display. The test strip
reader may further comprise a movable tray that holds a cassette,
which in turn holds the test strip under test. The movable tray may
be configured to accommodate cassettes of different sizes and from
different test manufacturers. The test strip reader may further
comprise a gear rack on the movable tray and a rotary damper in the
base portion including a pinion gear, with the gear rack engaging
the pinion gear during reading of the test strip.
[0012] The test strip reader may further comprise a bar code reader
in the base portion, wherein the barcode reader reads a barcode
from a cassette that holds the test strip in conjunction with
reading of the test strip.
[0013] The light source of the test strip reader may be a light
emitting diode. The test strip reader may further comprise an
illumination optical system that enhances the level of illumination
of the test strip. The illumination optical system may comprise at
least one spherical lens element and at least one hemispherical
lens element.
[0014] The test strip reader may further comprise a reading optical
system that directs at least some of the light reflected from the
test strip to the sensor. The reading optical system may comprise
at least one spherical lens element, and may comprise at least one
semi-cylindrical lens element. The sensor may be a first sensor,
and the test strip reader may further comprise a second sensor that
senses illumination from the light source directly, wherein the
electronic circuit is configured to adjust measurements of
reflected light taken from the first sensor, based on direct
measurements of light intensity taken from the second sensor, to
compensate for variations in the intensity of the light source
during reading of the test strip.
[0015] The test strip reader may comprise a battery that powers the
electronic circuitry. The electronic circuitry may be configured to
repeatedly take measurements of the light reflected from the test
strip during reading of the test strip, convert the measurements to
digital values, and to apply a predetermined set of interpretation
rules to the digital values in order to determine a test result.
The electronic circuitry may comprise a memory in which test data
are stored for later retrieval, and the memory may include a
removable memory.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 shows an exploded view of the optical and electronic
components of a test strip reader in accordance with an example
embodiment of the invention.
[0017] FIG. 2 shows an exploded view of the base and transport
mechanism of a test strip reader in accordance with an example
embodiment of the invention.
[0018] FIG. 3 shows the assembled reader with one wall cut away to
show the internal parts, in accordance with an example embodiment
of the invention.
[0019] FIGS. 4A-4D show upper left, lower left, upper right, and
lower right portions respectively of a schematic diagram of the
electronic circuit of a test strip reader in accordance with an
example embodiment of the invention.
[0020] FIG. 5 shows an optical path for a test strip reader in
accordance with another example embodiment of the invention.
[0021] FIG. 6 shows an example graphical representation of test
data gathered from a test strip by a reader according to an example
embodiment of the invention.
[0022] FIG. 7 shows a flowchart of the process for reading a test
strip designed to detect the presence or absence of avian
influenza, in accordance with an example embodiment of the
invention.
[0023] FIG. 8 shows the external appearance of a test strip reader
in accordance with another example embodiment of the invention.
[0024] FIG. 9 shows another view of the example reader of FIG.
8.
[0025] FIG. 10 shows a cutaway side view of the example reader of
FIG. 8.
[0026] FIG. 11 shows an end view of the transport mechanism and
other components in the example reader of FIG. 8.
[0027] FIG. 12 illustrates a simplified block diagram of the
electrical and electronic systems of the example reader of FIG.
8.
DETAILED DESCRIPTION OF THE INVENTION
[0028] The term "test strip" as used herein refers to any medium
used horizontally or vertically to accomplish a bioassay, drug
test, pregnancy test or other test reliant on the transport of a
fluid through or across that medium for the purpose of detecting
various constituents of the fluid.
[0029] Lateral flow devices are a preferred format. Similar to a
home pregnancy test, lateral flow devices work by applying fluid to
a test strip that has been treated with specific biologicals.
Carried by the liquid sample, the biologics are labeled and flow
through the strip and can be captured as they pass into specific
zones. The amount of label found on the strip is proportional to
the amount of the target analyte. The lateral flow typically
contains a solid support (for example nitrocellulose membrane) that
contains three specific areas: a sample addition area, a capture
area, and a read-out area that contains one or more zones, each
zone containing one or more labels. The lateral flow can also
include positive and negative controls. Thus, for example a lateral
flow device can be used as follows: target proteins are separated
from other proteins in a biological sample by bringing an aliquot
of the biological sample into contact with one end of a test strip,
and then allowing the proteins to migrate on the test strip, e.g.,
by capillary action. Proteins, antibodies, and/or aptamers are
included as capture and/or detect reagents. Methods and devices for
lateral flow separation, detection, and quantification are known in
the art, e.g., U.S. Pat. Nos. 6,942,981, 5,569,608; 6,297,020; and
6,403,383 incorporated herein by reference in their entirety.
[0030] One form of a lateral assay is a PDZ (Psd-95, D1g, and ZO1
proteins) capture assay. In such an assay, a PDZ protein or one
antibody or population of antibodies is immobilized to a solid
phase as a capture agent, and another antibody or population of
antibodies or a PDZ protein in solution is as detection agent. In
one format, a test strip comprises a proximal region for loading
the sample (the sample-loading region) and a distal test region
containing a PDZ protein capture reagent and buffer reagents and
additives suitable for establishing binding interactions between
the PDZ protein and any PL (PDZ ligand) protein in the migrating
biological sample. The selection of PDZ capture reagent and
antibody detection reagent depends on the target. Typically, the
detection agent is labeled, such as with gold. If an antibody
population is used, the population typically contains antibodies
binding to different epitope specificities within the target
antigen. Accordingly, the same population can be used for both
capture agent and detector agent. If monoclonal antibodies are used
as contact and detection agents, first and second monoclonal
antibodies having different binding specificities are used for the
solid and solution phase. Capture and detection agents can be
contacted with target antigen in either order or simultaneously. If
the capture agent is contacted first, the assay is referred to as
being a forward assay. Conversely, if the detection agent is
contacted first, the assay is referred to as being a reverse assay.
If target is contacted with both capture agent and detection agent
simultaneously, the assay is referred to as a simultaneous assay.
After contacting the sample with capture and detection antibodies,
a sample is incubated for a period that usually varies from about
10 min to about 24 hr and is usually about 1 hr. A wash step can
then be performed to remove components of the sample not
specifically bound to the detection agent. When capture and
detection agents are bound in separate steps, a wash can be
performed after either or both binding steps. After washing,
binding is quantified, typically by detecting label linked to the
solid phase through binding of labeled solution antibody. Usually
for a given pair of capture and detection agents and given reaction
conditions, a calibration curve is prepared from samples containing
known concentrations of target antigen. Concentrations of antigen
in samples being tested are then read by interpolation from the
calibration curve. Analyte can be measured either from the amount
of labeled solution antibody bound at equilibrium or by kinetic
measurements of bound labeled solution antibody at a series of time
points before equilibrium is reached. The slope of such a curve is
a measure of the concentration of target in a sample. Examples of
such assays for detecting pathogen analytes including the NS1
protein of influenza A or the E6 protein of HPV using PDZ proteins
to the PL motifs of these peptides as capture agents and antibodies
to other epitopes of these proteins as detection agents (or vice
versa) are described in e.g., US20072224594, WO 07/018,843/US
2005255460, WO 07/005,948 and WO2008048276.
[0031] The invention provides a device for sensing and reporting
the result of a test done on a test strip. With rapid response
becoming more important and field work requiring immediate results
to study outbreaks of new pathogens, a portable, inexpensive,
battery powered strip reader is desirable. The invention includes a
method and apparatus that takes advantage of small, inexpensive and
durable components. The components may be coupled with comparative
algorithms to improve on the accuracy of lateral flow strip tests,
and may significantly reduce false positive and false negative
results.
[0032] In one embodiment, the apparatus is contained in a
rectangular package measuring approximately 4.times.5.times.8
inches and has a printed circuit board mounted near the top of the
package that contains, among other components, two photo-detectors
that point down through an optics block. In one embodiment, the
optics block is made of black plastic, although other suitable
materials may be used. The optics block is attached to the circuit
board, for example with screws or other fasteners, and shields the
photodetectors from stray light. The lower end of the optics block
contains two acrylic spherical lenses that are one half inch in
diameter and are held into the block by a plate that also holds
four light emitting diodes that are mounted immediately beside the
lenses for the purpose of illuminating the test strip. Preferably,
the four light emitting diodes are configured in series so that
fluctuations in the current passing through them will affect all
four similarly. The test strip, contained in this embodiment within
a cassette, is placed in a cassette holder capable of holding two
cassettes simultaneously. The cassette to be tested is placed in
one position and a reference cassette is placed in the other
position so the device can comparatively monitor for any
fluctuations of light levels due to power or temperature
fluctuations, or effects of geometrical changes in the reader
resulting from movement of the mechanism. The base of the device
contains a mechanically-powered transport mechanism that is
activated by the operator by inserting the cassette holder into the
device as far as it will travel until stopped. This transport means
comprises a plate to receive the cassette holder, a spring that
propels the plate in order to push the cassette holder back out of
the device, and a damping means, in this case a small hydraulic or
pneumatic cylinder, that insures that the cassette holder moves
past the optics at a limited rate. The base further contains an
encoder that reads an encoder strip that is mounted on the
transport means in order to sense the intervals at which the strip
should be checked for a result. A bar code detector is mounted
below the transport means and is used to identify cassettes as they
enter the device in order to allow the device to record results in
a traceable manner.
[0033] A housing encloses the reader and accommodates connectors
for a charging power supply and USB connection as well as a switch
for power and an alphanumeric display to show results. A switch for
the display backlight is provided to conserve power.
[0034] The simplicity of the device and the use of a simple
positive or negative result (i.e. presence or absence, compared to
a defined threshold by the appropriate algorithm) allow the user to
effectively operate the device with little training, thereby
reducing operating costs.
[0035] In one embodiment, a plastic cassette containing a test
strip is placed into one of two wells in a cassette holder. The
other well contains a reference cassette for comparison of
illumination levels at any time to insure that changes in apparent
reflectance levels along the length of the strip is due to actual
reflectance differences and not a variation in the light level due
to power or temperature fluctuation or to geometrical changes
resulting from movement of the transport mechanism. As the cassette
holder is inserted into the device, an encoder is moved by the
transport mechanism. A photo-detector, within a slotted housing
beneath the cassette holder, allows the electronics to read a
barcode on the bottom of the cassette through a slot in the bottom
of the cassette holder. Once the cassette holder is inserted as far
as it will go into the device, the user releases the cassette
holder. A spring attached to a sliding member of the transport
mechanism propels the cassette holder in a reverse direction and
back out of the device at a controlled rate as governed by a
damping means acting against the spring. The transport mechanism is
thus mechanically-powered, and does not require electrical power.
The encoder tracks the motion of the cassette beneath the optical
elements and a processing unit interrogates the photo-detectors on
the main circuit board every time an encoder state changes. The
light level detected by each photo-detector is then recorded in
memory. This allows data on reflectance to be graphed by the
software and to be adjusted based on readings from the strip within
the reference cassette. It further allows the software to compare
the reflectance values of the test strip, as corrected for any
light fluctuations, to a set of algorithms to determine whether or
not the values compare to previously determined parameters in a way
that determines whether the test result is positive, negative or
invalid. The result is displayed on the alphanumeric display and
the raw data, including all reflected light levels at each point
along the test strip, are recorded in memory for later download,
via the USB port, into a separate computer for further study or
comparison to other studies if desired. In other embodiments, the
reference photo-detector does not require a separate cassette but
reads the light output fluctuations directly from the light source
or from a reflective element mounted near the light source. In
other embodiments, the one half inch diameter acrylic sphere is
replaced by a commercial lens or a sphere of a different diameter,
a different material, or both. In some embodiments, the optical
path has a greater total length in order to gain higher resolution
for tests that require it.
[0036] The invention finds use in clinical settings as well as in
the field. Its lower cost will make it attractive in settings that
may not require the limited size it offers. The fact that it is
small, light and battery powered makes it especially attractive to
users in rural areas of the world or in military settings that are
by their nature, on the move.
[0037] One preferred embodiment of the device is shown in FIGS. 1
through 4D. FIG. 1 shows an exploded view of the optical and
electronic components aligned above the cassette holder. A printed
circuit board 1 contains most of the circuit elements of the device
including a power supply, a processor, memory, a battery, an
amplifier circuit, I/O and two photo-detectors 2 that are capable
of detecting the specific wavelengths of light most useful in the
tests for which the specific reader is used. Photo-detectors 2 may
be, for example, model VTB1013BH available from PerkinElmer, Inc.,
of Waltham, Mass., USA. The photo-detectors are housed within a
plastic optics block 3 that is attached to the printed circuit
board 1 using two screws, not shown. At the end of the optics block
3 opposite the printed circuit board 1 are two holes that receive
lenses 4 that in this embodiment, are clear acrylic spheres, each
one half inch in diameter. These lenses 4 are held into the optics
block 3 by a plate 5 containing four LEDs 6 for the illumination of
the test strips. The plate 5 is attached to the optics block 3
using a screw, not shown. Below the plate 5 is shown a cassette
holder 7 that in turn contains a test cassette 8 to be tested, and
a reference cassette 9 for the monitoring of light level
fluctuations during a test.
[0038] FIG. 2 shows the assembly of the mechanism that transports
the cassette holder 7 into and out of the device. A base 10 having
a slot 11 supports a spring plate 12 having a slot 13. Two shoulder
screws 14 engage the slots (11 and 13) from bottom and top
respectively in the base 10 and the spring plate 12 for the purpose
of guiding the spring plate 12 in a linear motion when the cassette
holder 7 is inserted into the device. A pocket 15 in the base
houses a spring 16 and a damper means 17 that together, propel the
spring plate 12, and therefore the cassette holder 7 in a direction
opposite to its direction of insertion, at a controlled rate that
is readable by the optics and logic circuitry. An encoder strip 18
is attached to the spring plate 12 by means of a clamp 30, and is
read by the encoder 19 as the spring plate 12 moves. Encoder 19 may
be, for example, a model EM1-0-250 available from U.S. Digital of
Vancouver, Wash., USA. A barcode reader means 20 is recessed into
the base 10 next to the damper means and is used to identify each
test cassette 8 by reading a unique bar code label that has been
placed on the bottom surface of the test cassette 8. An open slot
in the cassette holder 7 beneath the test cassette 8 allows the
barcode reader means 20 an optical path to the barcode on the
bottom of the test cassette 8.
[0039] FIG. 3 shows the assembly of the internal components of the
device mounted onto the base 10 along with guides 21 and 22 that
control the path of the cassette holder 7 as it travels into and
out of the device. The cassette holder is positioned as it would be
just before entering the reader. The housing in this embodiment is
made up of separate plastic plates and comprises four walls and a
cover that are held together using screws. A back wall 23 and blank
side wall 24 serve only to provide structure and to omit light from
the device. A cover 25 contains a display 26 to indicate whether a
test is positive, negative or invalid. A front wall 27 having
cutout 28 allows for the entry of the cassette holder 7 while
keeping ambient light from interfering with the readings of the
device. A connector and switch wall 29 contains cutouts to accept
power and data connections as well as switches to activate the
device and the backlight of the display 26.
[0040] The example device is used by switching on the power and
inserting a test cassette 8 into the cassette holder 7 and in turn
inserting the cassette holder 7 into the cutout 28 of the front
wall 27 and pushing the cassette holder into the device. As the
test cassette 8 passes over the barcode reader means 20, the
barcode containing an identifier on the bottom of the test cassette
is read and the identifier is recorded in memory. Once the cassette
holder 7 has been pushed into the device as far as it will travel,
the cassette holder 7 is released by the user and the spring 16
propels it, via the spring plate 12 in the opposite direction at a
speed that is controlled by the damper 17. This motion causes the
test strip within the test cassette 8 to pass beneath a lens 4 in
the optics block 3 causing any indicating stripes on the test strip
to be projected onto the photo-detectors 2 on the circuit board.
During this process, the encoder strip 18 is passing through the
encoder 19 and causing pulsed signals to be sent to the processor
every time the spring plate 12 has progressed one encoder increment
(for example, one thousandth of an inch in the example embodiment).
Upon each encoder pulse, the processor interrogates the
photo-detectors 2 and enters a value into memory for both the test
cassette 8 and the reference cassette 9.
[0041] FIGS. 4A through 4D show a schematic diagram of the
electronic circuit of the device, in accordance with an example
embodiment of the invention. In this example, operation of the
reader is controlled by a model PIC18F6527 microcontroller
available from Microchip Technology, Inc., of Chandler, Ariz., USA.
Of course, any other suitable microcontroller or microprocessor
system may be used.
[0042] FIG. 5 shows an optical path for a strip reader in
accordance with another example embodiment of the invention. In the
configuration of FIG. 5, no reference strip is needed. A light
source 501 illuminates a strip under test 502. In the example
shown, light source 501 is a light emitting diode, but other kinds
of light sources may be used. At least some of the light reflected
from strip 502 passes through lens system 503. In this example,
lens system 503 comprises two plano-convex lens elements made of
glass, plastic, or other suitable material. Other lens arrangements
may be used having different numbers or kinds of elements. For
example, the simple ball lenses shown in the embodiment of FIG. 1
may be used in this embodiment as well.
[0043] At least some of the light passing through lens system 503
reaches a sensor 504. Sensor 504 may be, for example, a VTB1013BH
Process Photodiode available from PerkinElmer, Inc., of Waltham,
Mass., USA, or another kind of sensor. Sensor 504, possibly in
conjunction with support electronics, provides an electrical signal
indicative of the brightness of the light reaching it. In one
example embodiment, the signal is a voltage proportional to the
amount of light striking sensor 504. The voltage can be converted
to a digital value using an analog-to-digital converter.
[0044] A second sensor 505 is mounted with a direct view of light
source 501. Sensor 505 thus reads the brightness of light source
501 directly. Light source 501 is the same light source that is
illuminating strip 502, so sensor 505 obtains a direct reading of
the amount of light being supplied to strip 502. No reference strip
or additional light sources are required to obtain calibration
information. In one example embodiment, sensor 505 is identical to
sensor 504, and provides a signal that can be digitized by
circuitry similar that shown in FIGS. 4A-4D. Any variation in the
brightness of light source 501 is detected and can be compensated
by making compensating adjustments to the digital values obtained
via sensor 504. For example, if at some point in a test sensor 505
indicates that light source 501 has dimmed by 10 percent since the
beginning of a test, digital values obtained via sensor 504 at that
point in the test may multiplied by (1/0.9) so that the reflectance
of strip 502 is accurately noted and the recorded digital values
are not affected by variations in the light output of light source
501. Alternatively, an algorithm used to analyze the test data may
accommodate illumination variations in some other way. The output
signals of the two sensors may be separately scaled using analog
circuitry or adjustment of digital values derived from the two
signals.
[0045] FIG. 6 shows an example graphical representation 600 of test
data gathered from a test strip by a reader according to an example
embodiment of the invention. This particular graph shows data
gathered from a test strip designed to test for two kinds of
influenza. A test trace 601 records digital values read from the
strip under test, and represents the reflectance of the test strip,
shown on the Y axis, as a function of distance along the test
strip, shown in the X axis. The result of the test is indicated by
the existence and relative heights of peaks in certain regions of
trace 601, corresponding to parts of the strip containing
chemically sensitive materials. Each peak indicates the existence
of a line of lowered reflectance on the strip under test. In this
example, a higher reflectance results in a lower Y value, and a
lower reflectance results in a higher Y value, although the
opposite arrangement may be used. The full scale Y value in this
example is about 65,000 digital counts, but one of skill in the art
will recognize that this scaling is entirely arbitrary. In FIG. 6,
the X axis is graduated in counts of the encoder, and this scaling
is also arbitrary.
[0046] A linear second trace 602 is fit to points on trace 601 read
from areas of the test strip that do not have chemically sensitive
materials that may form lines, and therefore trace 602 represents a
"baseline" reflectance of the test strip. A second baseline 603 is
fit to other points where lines of lowered reflectance are not
expected, and provides a second baseline that may be used to
increase the confidence in the test result. Peak heights may be
measured from one or more of the baselines.
[0047] In the example of FIG. 6, three regions of interest are
investigated, corresponding to X-axis positions 120-270 (region 1,
covering a control line on the test strip), 300-400 (region 2,
covering a Flu A line on the test strip), and 460-560 (region 3,
covering a Flu B line on the test strip). In this example, peaks
are apparent in regions 1 and 2, but no peak is discernable in
region 3. This combination indicates the presence of influenza A
and the absence of influenza B.
[0048] Various data smoothing, peak finding, or other data filters
may be applied during the analysis of the digital values.
[0049] In another example embodiment, a test strip designed to
detect the presence or absence of avian influenza may be read and
interpreted. A flowchart of the process for reading an avian
influenza test strip is shown in FIG. 7. In step 701, the test
strip is read, and in step 702, a baseline value is determined. In
steps 703 and 704, a region of the test strip corresponding to a
control line is analyzed. If peak filter 704 fails (for example, no
peak is found, or a peak of an incorrect height is found), the test
is determined to be invalid and that result is communicated in step
705. If a valid control peak is found, a region of the test strip
corresponding to a first line is analyzed in steps 706 and 707. If
the conditions of peak filter 707 indicate that the test result is
negative, that result is communicated in step 708. As the test
continues, a region of the test strip corresponding to a second
line is analyzed in steps 709 and 710. If the conditions of peak
filter 710 indicate that the test result is positive, that result
is communicated in step 711. If the test results are not yet
ascertained, then a comparative analysis is performed at step 712,
and a positive or negative result is communicated at step 713 or
714, depending on the result of the comparative analysis. The
comparative analysis may also reveal that the test is invalid,
which is reported in step 715.
[0050] More details about the processing performed in the various
steps shown in FIG. 7 are described below. These details assume
similar ranges of values in the X and Y axes of a chart similar to
that of FIG. 6. One of skill in the art will recognize that data
scaled differently may be used, with appropriate adjustments to the
number thresholds used in the analyses.
[0051] The baseline value determined in step 702 is the minimum Y
value recorded between X values of 200 and 750.
[0052] The test is determined to be invalid in steps 703-705 if
either 1) in the range of X values between 140 and 270, no Y value
exceeds the baseline by 1850 counts or more, or 2) the local
maximum Y value found between steps 140 and 270 is not at least 100
counts higher than either of the Y values found 70 steps either
side of this local maximum Y value.
[0053] The analysis of line 1 (steps 706-708) takes place in a
region between X values of 325 and 450. The test is determined to
be negative if either 1) no Y value in this region exceeds the
baseline by 1850 counts or more, or 2) the local maximum Y value
found in this region is not at least 1000 counts higher than either
of the values read 70 steps either side of this local maximum. If
neither of these conditions is met (the test has not been
determined to be negative), the outcome of the test is not yet
ascertained. The first peak height (above the baseline value) is
recorded for later use.
[0054] The analysis of line 2 (steps 709-711) takes place in a
region between X values of 600 and 725. The test is determined to
be positive if the local maximum Y value in this region does not
exceed baseline value by at least 1850 counts. The test is also
determined to be positive (when the local maximum is more than 1850
counts above the baseline value) if the local maximum value in this
region is not at least 1000 counts higher than either of the values
read 70 counts either side of this local maximum. If the test is
not determined to be positive, the outcome is not yet determined,
and second peak height (above the baseline value) is recorded for
later use.
[0055] The comparative analysis (steps 712-715) operates on the
first and second peak heights previously recorded. If both the
first and second peak heights exceed the baseline value by 45,000
counts or more, the test is invalid. If the first peak height is
less than 30,000, and the first peak height is at least three times
the second peak height, the test is determined to be positive. If
the first peak height is less than 30,000, and the first peak
height is less than three times the second peak height, the test is
determined to be negative. If the first peak height is more than
30,000 and both peak heights are less than 45,000, then the first
and second peak heights are compared and the test is determined to
be 1) positive if the first peak height is higher than the second
peak height, and 2) negative otherwise. If the first peak height is
greater than 45,000 and the second peak height is less than 45,000,
the test is determined to be positive. If the first peak height is
less than 45,000 and the second peak height is greater than 45,000,
the test is determined to be negative.
[0056] The example of FIG. 7 illustrates the basic principles of
test strip interpretation. Other tests may produce test strips with
different numbers of lines (and regions to analyze), and the
results of those tests may be interpreted by application of a
different set of rules.
[0057] It is understood that the examples and embodiments described
herein are for illustrative purposes only and that various
modifications or changes in light thereof will be suggested to
persons skilled in the art and are to be included within the spirit
and purview of this application and scope of the appended
claims.
[0058] For example, while the system of FIG. 1 has been illustrated
as using four light emitting diodes as light sources, other
quantities and kinds of light sources may be used, such as one or
more fluorescent lamps, incandescent lamps, or other sources.
Preferably, the light source is selected to emit light with
wavelengths that will reveal significant contrast in the test strip
being read as sensed by the light sensor or sensors. For example,
if a particular test checks for the presence or absence of a red
stripe on an otherwise white background, green light emitting
diodes may be an appropriate light source, as the white background
will reflect most of the green light, while the red stripe will
reflect less.
[0059] In another example, the housing depicted in the example
embodiment shown in the drawings is made of separate plastic
plates. In other embodiments, the housing may be made of one or
more injection molded plastic parts, folded sheet metal parts,
die-cast parts, or parts made by other processes and connected
using screws, bolts, snap fits, adhesives, or other suitable
fastening methods.
[0060] While an alphanumeric display has been described, other
kinds of result indicators may be used. For example, the reader may
comprise a backlit liquid crystal display, a reflective liquid
crystal display, a display forming characters using light emitting
diode segments, or other kinds of displays. Alternatively, the
display may be configured to display more than simply a test
result, and may allow display of the reflectance data from a test
in graphical form. Or a result indicator may be as simple as one or
more lights that indicate a positive or negative test result. For
example, a reader may simply illuminate a red light to indicate a
negative result and illuminate a green light to indicate a positive
result. Many other configurations are possible.
[0061] The circuit schematic in FIGS. 4A-4D shows but one example
of a circuit for controlling a reader in accordance with an example
embodiment of the invention. Many other circuit configurations are
possible, using any of many kinds of processors, memory, analog
circuits, digital circuits, and the like.
[0062] FIGS. 8-11 show a test strip reader 800 in accordance with
another example embodiment of the invention.
[0063] FIG. 8 shows the external appearance of the reader in
accordance with this embodiment. The reader comprises a base
portion 801 and an upper portion 802. Upper portion 802 includes a
display 803, which may be, for example, a touch screen display
capable of displaying data, text, images, and other kinds of
output, and also capable of receiving user input via touches on the
surface of the display 803. In one embodiment, display 803 can
display 128.times.128 pixels. Display 803 may be a reflective
liquid crystal display (LCD), a backlit LCD, or another kind of
display. Display 803 is positioned at an angle from horizontal for
easy viewing by a user of reader 800. For example, display 803 may
be positioned at an angle between 30 and 60 degrees from
horizontal, and preferably at an angle between 40 and 50
degrees.
[0064] Base portion 801 includes a sliding cassette holder or tray
804, which is shown holding a cassette 805. Cassette 805 includes a
test strip 811, which is to be read by reader 800. Preferably,
cassette 805 also includes a bar code on its bottom side for
identification purposes as has been previously described. Also
shown in FIG. 8 is a second cassette 805a, inverted to show its
bottom side, which includes a bar code 812. Preferably, tray 804 is
sized to accommodate cassettes of various sizes and from different
test manufacturers. Tray 804 may include a pushing surface 806,
upon which a user may conveniently push when inserting the tray and
cassette into the reader so that a test can be performed. FIG. 9
shows test strip reader 800 with the tray 804 and cassette 805
fully inserted. (Cassette 805 is not visible in FIG. 9.)
[0065] Base portion 801 may comprise one or more electrical
connectors, switches, card slots, or other devices for controlling,
communicating with, or adding capabilities to the reader. Example
reader 800 includes an RS-232 serial port connector 807, a
universal serial bus (USB) connector 808, and a power switch 809,
all located in recessed connector panel 810. Merely by way of
example, an external printer may be connected to the RS-232 port so
that test results or other information can be printed. A computer
may be connected to the USB port for downloading firmware upgrades
or other data to the test strip reader 800, retrieving stored test
data from reader 800, or other uses. Many other kinds of interfaces
may be used, to communicate with these and other kinds of devices.
A memory card slot 813 may be positioned on connector panel 810, or
at another location. For example, memory card slot 813 may accept a
removable solid state memory card, such as a flash memory card.
Reader 800 may store test data or results in the memory card, and
the card may be moved to a computer or other device for retrieval
of the data.
[0066] FIG. 10 shows a cutaway side view of example reader 800. A
main printed circuit board 1001 is mounted directly behind display
803. Of course, other mounting positions may be used. Main circuit
board 1001 may comprise a control circuit similar to that shown in
FIGS. 4A-4D. The control circuit preferably includes a
microprocessor and associated support circuitry, such as any needed
memory, clock, input/output or other circuitry. Alternatively, a
single-chip microcontroller may be used. In one example,
embodiment, a PIC24FJ256GA110 microcontroller available from
Microchip Technology, Inc., of Chandler, Ariz., USA, may be used.
The control circuit also preferably includes driving circuitry for
displaying data and receiving input from touch screen display 803,
circuitry for communicating over various input/output interfaces,
such as RS-232 port 807 and USB port 808, and circuitry for
controlling, reading, and communicating with the various other
components of the reader discussed below.
[0067] One of skill in the art will recognize that various cabling
and connectors may be used to interconnect the various reader
components and subsystems. The cabling and connectors have been
omitted from the figures for clarity of illustration. The
electronic circuitry of reader 800 preferably receives power from a
battery or an external power source. The battery may be a
rechargeable battery, rechargeable from an external power source,
and the reader may be configured to operate on battery power alone,
or from the external power source while the battery is recharging.
These power subsystems have also been omitted from the drawings, in
the interest of clarity. One of skill in the art will recognize how
to integrate them with a reader such as reader 800.
[0068] During reading of a test strip, a light source such as light
emitting diode (LED) 1002 emits light to illuminate the test strip
at reading location 1005. LED 1002 may be, for example, a model
LedEngin LZ1-00G105 distributed by Mouser Electronics, producing
light at a primary wavelength of about 536 nanometers. Other kinds
and colors of light sources may also be used. In example reader
800, an illumination optical system directs light from LED 1002 to
the test strip, to improve the illumination level at the test
strip. In one embodiment, the illumination optical system comprises
a plano-convex lens 1003 and a spherical lens 1004. (Even though
part of lens 1004 is cut away for assembly purposes, lens 1004 is
still considered to be a spherical lens because its primarily
functional surfaces are portions of a sphere.) Plano-convex lens
1003 may be a hemispherical lens. The radii of the curved surfaces
of lenses 1003 and 1004 may be, for example about 12.7 millimeters
(1/2 inch). The lenses may be made of glass, plastic, or any other
suitable material. Other kinds of optical systems may be used for
concentrating light from LED 1002 onto the test strip being read,
including lenses, reflectors, and other kinds of optical elements,
alone or in any combination.
[0069] The intensity of the reflected light is an indication of the
reflectance of the test strip at reading location 1005. Some of the
light reflected from the test strip reaches a first sensor 1006,
which, possibly in conjunction with support electronics, produces a
signal indicating the intensity of light falling on it. First
sensor 1006 may be, for example, a VTB1013BH Process Photodiode
available from PerkinElmer, Inc., of Waltham, Mass., USA, or
another kind of sensor. In one example embodiment, the signal is a
voltage proportional to the amount of light striking sensor 1006.
The voltage can be converted to a digital value using an
analog-to-digital converter.
[0070] A reading optical system may be used to direct some of the
light reflected from the test strip to first sensor 1006. In
example reader 800, a spherical lens 1007 helps gather and redirect
light from reading location 1005. (Part of lens 1007 may be cut
away for assembly purposes, but lens 1007 may still be considered
to be a spherical lens because its primarily operative surfaces are
portions of a sphere.) Lens 1007 may have a radius, for example of
about 19.05 millimeters (3/4 inch), and may be made of glass or
plastic. Other kinds of lenses may be used, for example a system
similar to the two plano-convex elements in lens system 503
discussed above, or another kind of lens system. In one example
embodiment, a lens system similar to lens system 503 may include
lens model numbers ASR-038-03 and ASR-0805, made of poly methyl
methacrylate (PMMA), and available from Align Optics or from Anson
Optical. The portion of lens 1007 that is used to direct light may
be limited to a transmission band 1008 around lens 1007.
Preferably, the portion of lens 1007 in transmission band 1008 has
a polished surface. Transmission band 1008 may be, for example,
about 12.7 millimeters (1/2 inch) wide and may girdle lens 1007 at
the optical axis of the reading optical system. The remainder of
the surface of lens 1007 may be configured to reduce stray light
reflections, and is preferably given a matte finish, and covered
with a light-absorbing coating, such as black paint.
[0071] One or more baffles or other devices such as tube 1009
(shown in cross section) may be included for further reducing stray
light reflections that may detrimentally affect the reading of
first sensor 1006. In reader 800, a second lens 1010 is also
included. Lens 1010 is a semi-cylindrical lens, shown with its axis
cross-ways to the viewing direction of FIG. 10. The curved surface
of lens 1010 may have a radius, for example, of about 10
millimeters. Additionally, a small aperture 1011 may be placed
immediately in front of sensor 1006, between lens 1010 and first
sensor 1006. For example, a slit aperture with a width of about
0.75 millimeters (0.030 inches) may be molded into an opaque
plastic part that resides in front of first sensor 1006.
[0072] During reading of a test strip, the signals from sensors
1006 and 1016 are repeatedly read by the microprocessor while the
test strip is transported through the reader and past reading
location 1005. A second sensor 1016 produces a signal indicative of
the intensity of LED 1002. Second sensor 1016 may be the same kind
of sensor as first sensor 1006, or another kind of sensor. Light
from LED 1002 reaches second sensor 1016 directly, and therefore
second sensor 1016 serves as a light monitor. Here, "directly"
means that light from LED 1002 reaches second sensor 1016 without
first reflecting from the test strip under test or from a
calibration or monitor strip. At least some of the light reaching
second sensor 1016 may reflect from stationary surfaces, refract
through certain elements of reader 800, or reach sensor 1016 in
some circuitous way and still be considered to have been received
directly. Readings from second sensor 1016 are taken in concert
with the readings from first sensor 1006, and used to adjust the
readings from first sensor 1006 to account for variations in the
intensity of LED 1002.
[0073] Cassette holder or tray 804 preferably includes an encoder
strip 1012, configured to pass through encoder reader 1013 during
motion of tray 804. Encoder strip 1012 may be, for example, a thin,
flat metallic strip with regularly-spaced linear openings through
it, or may be a clear plastic strip with opaque lines applied
photographically. Encoder reader 1013 includes a light source and a
detector on opposite sides of encoder strip 1012, and senses the
alternate blocking and passing of light from the light source to
the detector as encoder strip 1012 passes. Alternatively, encoder
strip 1012 may have a contrasting pattern printed on an opaque
material, and encoder reader 1013 may read encoder strip 1012
entirely from one side. Encoder strip 1012 may include enough slits
or lines so that a pulse or state change occurs every 0.004 inches
(0.1 millimeters), every 0.001 inches (0.025 millimeters), or
another suitable travel distance of encoder strip 1012. For
example, encoder strip 1012 may include lines or slits 0.008 inches
(0.20 millimeters) wide every 0.016 inches (0.40 millimeters), from
which a quadrature reader produces a state transition every 0.004
inches (0.10 millimeters). Signals from encoder reader 1013 are
passed to the microprocessor, which uses the encoder signal to
determine when to take light intensity measurements. For example,
light intensity measurements may be taken each time a change in
state of the encoder signals occurs, every other time, every third
or fourth time, or at some other regular or irregular interval.
Sensors 1006 and 1016 may be read at the same or different
transport mechanism positions. Other kinds of encoders or position
indication means may also be used, for example a rotary encoder.
Alternatively, tray 804 may be driven with a stepper motor, and a
count of the step position of the motor may serve as a position
indicator.
[0074] Test strip reader 800 may also include a bar code reader
1014 and an associated bar code illuminator 1015. Bar code
illuminator 1015 may be, for example, a light emitting diode (LED)
that illuminates the bottom side of cassette 805 as it passes, and
bar code reader 1014 may be any suitable optical detector for
reading the bar code from the bottom of cassette 805. Signals from
bar code reader 1014 are preferably also passed to the
microprocessor, so that the bar code information can be correlated
with the results of the test.
[0075] FIG. 11 shows an end view of the transport mechanism and
other components in base portion 801. The transport mechanism
preferably is a passive mechanical system including a spring 1104
and a damper 1103. In a preferred embodiment, a user pushes tray
804 carrying cassette 805 into reader 800. Tension spring 1104
resists the motion, and is elongated during the inward motion. Once
tray 804 is fully inserted, the user may release it to be pulled
back out of reader 800 by spring 1104. Tray 804 is constrained to
move in a linear motion by mechanical guides 1101. Encoder strip
1012 is attached to one side of tray 804. Attached to another side
of tray 804 is a gear rack 1102. During motion of tray 804, gear
rack 1102 actuates rotary damper 1103 through pinion gear 1106,
engaged with rack 1102. Spring 1104 is placed to pull tray 804
outward from reader unit 800. Rotary damper 1103 resists motion of
tray 804, and limits the speed at which spring 1104 can pull tray
804 out. Bar code reader 1014 and bar code illuminator 1015 are
positioned under tray 804, and attached to a bar code and encoder
circuit board 1105. Bar code and encoder circuit board 1105
communicates with main circuit board 1001 so that the
microprocessor can monitor the position of tray 804 and can read
the bar code from the bottom of cassette 805.
[0076] FIG. 12 illustrates a simplified block diagram of the
electrical and electronic systems of reader 800. A microprocessor
or microcontroller 1201 provides control, computation, and user
interface functions for the system. Microcontroller 1201 may
include an arithmetic logic unit (ALU), memory, and input/output
circuitry, including one or more analog-to-digital converters
(A/D). The memory may comprise various kinds of memory in any
suitable combination, including volatile memory such as random
access memory (RAM), nonvolatile memory such as read only memory
(ROM), flash memory, programmable read only memory (PROM), erasable
programmable read only memory (EPROM), and electrically erasable
programmable read only memory (EEPROM), and may also include long
term storage devices.
[0077] Microcontroller 1201 interfaces with touch screen display
803 to communicate with the user of reader 800, receive commands,
display test results, and provide other functions. Microcontroller
1201 controls the operation of main illumination LED 1002.
Microcontroller 1201 also communicates with encoder reader 1013,
and the components associated with reading bar codes from a
cassette, so that microcontroller 1201 can monitor the progress of
tray 804 through reader 800, and can associate the bar code read
from a cassette 805 with a test result. Microcontroller 1201 also
takes readings from first light sensor 1006, reading light
reflected from the test strip, and takes readings from second
sensor 1016, reading the intensity of LED 1002 directly.
Microcontroller 1201 uses the readings from the light monitor
sensor 1016 to adjust readings from the main sensor 1006 to account
for variations in the intensity of the light supplied to the test
strip. Microcontroller 1201 also interfaces with various
input/output ports 1203, such as RS-232 serial port 807, USB port
808, and any other ports provided. Microcontroller 1201 may also
communicate with removable memory 1204, which may be, for example a
removable card containing flash memory or the like.
[0078] A power subsystem 1202 provides power to microcontroller
1201 and the various other devices and systems through connections
not shown. Power system 1202 may include a battery, so that reader
800 may be operated in a remote location. The battery may be
rechargeable.
[0079] It will be understood that certain steps in methods
described herein may be performed by a computer, microprocessor,
microcontroller, or other processor executing a stored program
stored on a computer readable medium. A computer readable medium
may comprise memory such as random access memory (RAM), read only
memory (ROM), flash memory, erasable programmable read only memory
(EPROM), volatile memory, nonvolatile memory, or the like, or
combinations of these. A computer readable medium may comprise mass
storage, such as a compact disc read only memory (CD-ROM), a
digital versatile disk (DVD), magnetic storage, magneto-optic
storage, or the like, or combinations of these.
[0080] All publications, patents and patent applications cited
herein are hereby incorporated by reference in their entireties for
all purposes to the same extent as if each individual publication,
patent or patent application were specifically and individually
indicated to be so incorporated by reference. Unless otherwise
apparent from the context any feature, embodiment, element, or step
can be used in combination with any other.
* * * * *